The present invention relates generally to air compressors and, more particularly, to a compressor having variable geometry inlet nozzle and diffuser assemblies. II. Description of the Prior Art
There are a number of previously known turbine compressors which comprise a housing having a centrifugal impeller which is rotatably mounted within the housing. An inlet passageway extends from one axial end of the impeller and to an inlet formed in the housing. The impeller is rotatably driven by any conventional means and, in doing so, inducts air through the inlet passageway and discharges compressed air through a diffuser passageway extending radially outwardly from the other end of the impeller.
In many applications, it is desirable to vary both the pressure output and air flow rate from the compressor. In order to achieve variable pressure and flow output from the compressor, many of the previously known devices vary the rotational speed of the impeller until the desired pressure and flow output is obtained.
Furthermore, it is often desirable to combine the compressor with an electrical generator, for example, when the electrical generator and compressor are employed as a start cart for starting and/or servicing aircraft engines. Different aircraft engines, of course, require different pneumatic pressures and air flow rates.
In a start cart, the electrical generator and compressor are typically driven by a single motor. The electrical generator, however, must be driven at a substantially constant speed in order to provide an alternating current electrical output at a predetermined frequency, typically 400 hertz. Conversely, the compressor must be driven at different rotational speeds in order to match the required pressure and air flow output of the compressor to the aircraft engine. Consequently, these previously known start carts have employed either a hydrostatic transmission to mechanically maintain a constant generator speed or they have employed a variable speed, constant frequency (VSCF) system coupled to the generator output which electronically converts a variable frequency output from the generator to a constant frequency output.
These previously known hydrostatic transmissions and VSCF systems, however, are not only expensive in construction but also degrade the overall power efficiency of both the start cart compressor and electrical generator systems.